Learning to Pivot as a Smart Expert

Linear programming has been practically solved mainly by simplex and interior point methods. Compared with the weakly polynomial complexity obtained by the interior point methods, the existence of strongly polynomial bounds for the length of the pivot path generated by the simplex methods remains a mystery. In this paper, we propose two novel pivot experts that leverage both global and local information of the linear programming instances for the primal simplex method and show their excellent performance numerically. The experts can be regarded as a benchmark to evaluate the performance of classical pivot rules, although they are hard to directly implement. To tackle this challenge, we employ a graph convolutional neural network model, trained via imitation learning, to mimic the behavior of the pivot expert. Our pivot rule, learned empirically, displays a significant advantage over conventional methods in various linear programming problems, as demonstrated through a series of rigorous experiments

Developing a Modeling Framework for Nonstationary Urban Hydraulic Analyses

Multiple recent national and international climate assessment reports suggest that the frequency, duration and intensity of future extreme precipitation in the North East US will increase. Urban cities in this region like Philadelphia are extremely vulnerable to these impacts due to their combined sewer overflows (CSO). These are mainly due to the fact that the sewer systems receive higher than normal flows during heavy precipitation. Hence, they seek to incorporate the best available information about current and future climate and understand the extent of their impacts on their stormwater network. This project intends to develop a general modeling framework for integrating multiple sources of information such as rain gauge data and climate scenarios for extreme rainfall events with prescribed duration using a Hierarchical Bayesian modeling technique. It aims to develop a stochastic temporal rainfall field simulator for the analysis of the extreme rainfall precipitation events. The approach here is to minimize uncertainties in stationary hydraulic assessment models with non-stationary ones. Five extreme rainfall models were developed for improvements with both stationary and non-stationary modeling frameworks. Recommendations and evaluations of these model outcomes are evaluated and discussed to provide a critical path towards informing climate adaptation decision on the ground.M.S., Environmental Engineering -- Drexel University, 201

Outflows from active galactic nuclei: The BLR-NLR metallicity correlation

The metallicity of active galactic nuclei (AGNs), which can be measured by emission line ratios in their broad and narrow line regions (BLRs and NLRs), provides invaluable information about the physical connection between the different components of AGNs. From the archival databases of the International Ultraviolet Explorer, the Hubble Space Telescope and the Sloan Digital Sky Survey, we have assembled the largest sample available of AGNs which have adequate spectra in both the optical and ultraviolet bands to measure the narrow line ratio [N II]/H{\alpha} and also, in the same objects, the broad-line N V/C IV ratio. These permit the measurement of the metallicities in the NLRs and BLRs in the same objects. We find that neither the BLR nor the NLR metallicity correlate with black hole masses or Eddington ratios, but there is a strong correlation between NLR and BLR metallicities. This metallicity correlation implies that outflows from BLRs carry metal-rich gas to NLRs at characteristic radial distances of ~ 1.0 kiloparsec. This chemical connection provides evidence for a kinetic feedback of the outflows to their hosts. Metals transported into the NLR enhance the cooling of the ISM in this region, leading to local star formation after the AGNs turn to narrow line LINERs. This post-AGN star formation is predicted to be observable as an excess continuum emission from the host galaxies in the near infrared and ultraviolet, which needs to be further explored.Comment: 19 pages, 13 figures, 3 tables. Accepted for publication at MNRA

catena-Poly[[[bis­[2,2′-(propane-1,3-diyl­dithio)bis­(1,3,4-thia­diazole)-κN 4]copper(II)]-bis­[μ-2,2′-(propane-1,3-diyldithio)bis­(1,3,4-thia­diazole)-κ2 N 4:N 4′]] bis­(perchlorate)]

In the title compound, {[Cu(C7H8N4S4)4](ClO4)2}n, the CuII atom, occupying a crystallographic inversion centre, is six-coordinated by six N atoms of three symmetry-related 2,2′-(propane-1,3-diyldithio)bis­(1,3,4-thia­diazole) (L) ligands in a slightly distorted octa­hedral geometry. The ligand L adopts two kinds of coordination modes in the crystal structure; one is a monodentate coordination mode and serves to complete the octa­hedral coordination of the Cu atom and the other is an N:N′-bidentate bridging mode in a trans configuration, bridging Cu atoms via translation symmetry along the b axis into a chain structure. The perchlorate ions serve as acceptors for inter­molecular C—H⋯O hydrogen bonds, which link the chains into a three-dimensional network

Application of Fibonacci Sequence and Lucas Sequence on the Design of the Toilet Siphon Pipe Shape

The purpose of this study was to explore the method for designing the toilet siphon pipe shape to improve flushing performance. The Fibonacci sequence and the Lucas sequence were used to design the structural parameters of the siphon pipe. The flushing processes of the toilet were simulated using the computational fluid dynamics (CFD) method to analyze the flushing performance under different siphon pipe shapes. Experimental studies were conducted to verify the reliability of the simulation results. The results indicated that when the Lucas numbers and the Fibonacci numbers were utilized to regulate the curvature of the siphon pipe in the Xi direction and the Yj direction respectively, the flushing performance of the toilet was optimal. In order to obtain better flushing performance, the curvature of the siphon pipe should be smooth and have obvious transitions at the connections of different sections. When the overall size of the siphon pipe is kept constant, a short siphon pipe length is helpful for the improvement of toilet flushing performance

Poly[[tris­[μ-2,2′-(butane-1,4-diyl­dithio)bis­(1,3,4-thia­diazole)-κ2 N 4:N 4′]copper(II)] bis­(perchlorate)]

In the title compound, {[Cu(C8H10N4S4)3](ClO4)2}n, the CuII atom is located on a threefold inversion axis coordinated by six N atoms of symmetry-equivalent 2,2′-(butane-1,4-diyl­dithio)bis­(1,3,4-thia­diazole) ligands in a slightly distorted octa­hedral geometry. Adjacent CuII atoms are linked by the bridging bidentate thia­diazole ligands, which are situated about inversion centers. This leads to the formation of a three-dimensional network structure

Vitamin D intake and type 2 diabetes risk: a meta-analysis of prospective cohort studies

Background: The findings form studies on the relationship between vitamin D and type 2 diabetes were inconsistent.Objectives: To elucidate the association between vitamin D consumption and type 2 diabetes risk by conducting a metaanalysis.Methods: We conducted a systematic literature search to identify prospective cohort studies of vitamin D intake and type 2 diabetes risk prior to November 2012. Eligible studies were retrieved via both computer searches and manual review of references. The summary risk estimates were calculated based on the highest versus the lowest categories.Results: Meta-analysis of 4 prospective cohort studies involving 187, 592 participants and 9, 456 incident cases showed an absence of significant association between total vitamin D intake and type 2 diabetes risk. The combined RR was 0.93 (95% CI: 0.85–1.01). The associations were similar for subgroup analyses, a combined RR respectively was 0.94 (95% CI: 0.77-1.08), 0.91 (95% CI: 0.77-1.08), 0.93 (95% CI: 0.84-1.02), and 0.92 (95% CI: 0.84–1.01) for the intake of dietary vitamin D, supplemental vitamin D, total vitamin D in USA and total vitamin D for women only.Conclusions: Our results support that there was no association between vitamin D intake and type 2 diabetes.Keywords: Vitamin D, Diet; Type 2 Diabetes, Meta-analysisAfrican Health Sciences 2013; 13(4): 1130 - 113